Granule type acoustic transducer



Feb. 12, 1952 D. E. SKELTON 2,585,052

GRANULE TYPE ACOUSTIC TRANSDUCER Filed April 21, 1949 2 SHEETSSHEET 1 si 3 k 18 9 16 S IO? 6 BY W ATTORNEY Feb. 12, 1952 SKELTQN 2,585,052

GRANULE TYPE ACOUSTIC TRANSDUCER Filed April 21, 1949 2 SHEETS-SHEET 2INVENTOR DENNIS E. SKELTON BY W ATTORNEY Patented Feb. 12, 1952 UNITEDsrAr-Es PATENT. QFFIZCE...

I V 2,585,052 I GRANULE TYPE. ACOUSTIC TRANSDUCER. Dennis'Edward'Skelton, London; England; as"- signor to International Standard ElectricCorporation', New York, N. Y1, a corporation of DelawareApplicationApriI 21, 1949, Serial N 0. 88,770 InGi'eatBritain April 23,1948 (C1. Hik -123 l'Cl'aim.

This invention relates'to granule -type acoustic transducers.

The object'of the=inventiorr is to provide such transducers which aresimple and cheap to manufacture;

One feature of the'invention isa granule-type acoustic transducer inwhich both the electrodes are thin diaphragms' suitably protected fromdamage;

According to another feature of the invention there is proVided agranule-type acoustic transducer=comprising aca'sing member on or inwhich are -mounted all' otherparts and which forms the peripheral wallof the granule chamber; seatings for front and'back electrodes, and aperipheral seating for. the diaphragm which is operatively associatedwith the front electrode.

The invention will be particularlydescribed with reference to twoembodiments: shown in the accompanying drawings in which:

Fig. l is a cross section through a telephone type transmitterconstructed'in accordance with the first embodiment of the" invention,and

Fig; 2' is a part cross sectional view of'those portions'of atransmitter according to thesecnd embodiment of the invention" whichdiffer from corresponding portions shown in Fig. 1;

The transmittershownin' Fig. 1 of the 'accom panying' drawingscomprisesa' die-cast zinc or aluminum casing member which comprises anannulardisc'portion' I, a" peripheral annular portion 2 joined tothejportionlby a cylindrical portion 3. The portion 2 carries acylindrical extension 4- on the opposite side thereof from thecylindrical'portion 3T disc portion I carries an electrode chamberportion} with front and rear electrode faces 6, I and front and rearcylindrical extensions 8, 9 defining electrode-fixing recesses I0, II.

The front and rear electrodes each comprise an annular peripheralportion and a central domed portion, respectively numbered I2, I3 andI4, I5. Both electrodes are made of carbonised nickel for example, inthe manner described in British Patent No. 594,116, dated January 29,1948. The front electrode is of the order of .003 inch on its inner edgethe thick while the back electrode is of the order of electrodescapable-of manufacture by the same process from-similar'material.

The front electrode I2, I3 is fixed against its seating 6' by acold'flowing lead ring I5 in therecess II]. The lead ring technique isdescribed and claimed in copending U. S. patent -applica-- tion No.627,945, filed November 10, 1945;- issued September 12, 1950, as PatentNo. 2,521,744;

The lead ring I6 also positions an annular disc I! shaped internally andperipherally at I8, I9-to fit over the portions 8 and 3; 2, respectivelyof casing member. Disc [1 is preferably of aluminium alloy and of theorder of .003 inch'thick; Disc I'Ihas three equally spaced areas such as20, of the order of 0.1 inch in diameter punched to form a fine metalmesh of nutmeg grater form" constituting an acoustic resistance whichcan be adjustedafter punching by compressing the prongs of the mesh asdesired. The mesh resistance is considered preferable to theconventional silk-covered holes.

The diaphragm is of conventional design'but is axially apertured to forma substantially cylindrical ring of teeth 22 fitting into the interiorof the domed portion I3- of the front electrode as described and'claimedin copending U. S. patent" application No. 704,965, filed October 22,1946, issued January 30, 1951', as Patent No. 2,539,483. The centralaperture in the diaphragm is closed by a disc 23'to prevent ingress ofmoisture be-'- tween the diaphragm teeth 22 and the front electrodesurface.

The diaphragm 2| is peripherally heldbetween' the casing portion 4' anda' die-cast ormoulded apertured disc 24: 24 are fixed to the casing by aclamp ring 25 spun over the disc and casing portion 2, 4. The ring 25may be of brass but preferably will be of the thermo-plastic material.

The rear electrode I4, I5 contrary to usual practice is thin and fragileand in consequence needs protection which is provided by a back coverplate 26 of for instance nickel silver of the order of 0.02 inch thick.

It is necessary to electrically insulate the back electrode I4, I5 andits cover 26 from the frame I-d. For this purpose the diameter of thesetwo members is less than the diameter of the recess I I in which theyare mounted and an annular insulating ring 21 for instance of mica isinserted between the face I of the frame and the back electrode. Anannular ring 28 for instance of resin-bonded canvas is placed over thecover plate 26 and the back electrode assembly is secured by a lead ring29 in the manner described Thediaphragm 21 and disc" 3 and claimed incopending U. S. patent application No. 627,945, filed November 10, 1945,issued September 12, 1950, as Patent No. 2,521,744. The lead ring may bepressed from sheet but probably the best way is to uselead wire cut tolength and formed into a ring.

It will be noted that the back electrode l 4, l5 and its cover 26 are soshaped relatively that the cover will be guided by the electrode domeinto correct relation with the back electrode. The back electrode l4, l5and its cover 26 may be made into a subassembly prior to assembly intothe transmitter.

The plane annular face of the front electrode l2, l3 on the convex sidethereof and the carbon chamber peripheral surface 30 by the frameportion 5 are insulated preferably by brushing on white cellulose enameland allowing to dry in order to concentrate the electrical conductingpath across the carbon chamber to the zone between the domed portionsI3, l5 of the electrode.

The zinc or aluminium die-cast casing 9 is in electrical circuit withthe front electrode H! by contact of same with a portion of the casing,another portion of which is coated with a colloidal suspension of carbonor a silver paste and stored prior to assembly to assure a good contactsurface for the contact spring when the device is assembled inthetransmitter housing of a bandset, for instance.

The casing portion 5 is provided with a filling hole 32 through whichcarbon granules or the like are introduced with the carbon chamber. Theouter end of the filling hole is of greater diam eter than the rest toreceive a closure disc 33 sealed in position with, for instance, a massof clay shellac cement 34.

In assembling the transmitter, the back electrode assembly 21, l4, I5,28 is first inserted into the frame recess l l and secured by lead ring29. The clamping face of the front cover 24 is coated with sealingcompound after which the diaphragm 2| and the front cover 24 arepositioned and secured with clamping ring 25.

The granule chamber is now filled with carbon or the like on a shakingmachine, after which the filling hole is closed.

In Fig. 2 the second embodiment of the invention is shown. In this thereis provided a filling hole 34 in theback cover plate 35 and the space 36behind. the apertured back electrode 31 is used as a granule reservoir.The aperture in the back electrode has a turned edge so as to preventduring operation the flow of current to it. Once again the backelectrode assembly (in this case the members 21, 31, 35, 28) may befirst inserted into the frame recess H as a whole, the assembly beingsecured by the lead ring 29. In this embodiment of the invention a metaldisc 38 is placed on the back cover plate after completion of thefilling operation and its edges are crimped as shown at 39.

The diaphragm 2| in either embodiment may be formed of plastic materialexcept for the toothed hub which would be of metal moulded or connectedto the plastic diaphragm.

While I have described above the principles of my invention inconnection with specific apparatus, and particular modifications thereofit is to be clearly understood that this description is made only by wayof example and not as a limitation on the scope of my invention.

What I claim is:

A granule-type acoustic transducer having a metallic diaphragmconstituting the movable front electrode and another metallic diaphragmconstituting the relatively stationary back electrode, means forelectrically insulating said electrodes from each other, means wherebysaid electrodes are arranged in spaced relationship, said back electrodehaving a centrally located aperture of such size as to permit freepassage of granules therethrough, a cover plate, means for peripherallymounting said cover plate adjacent said back electrode to define achamber communicating through said aperture in the back electrode withthe zone between the electrodes, and granules substantially filling saidzone and chamber.

DENNIS EDWARD SKELTON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,186,746 Chisholm June 13, 19161,496,919 Bellus June 10, 1924 2,042,822 Bennett June 2, 1936 2,331,044Pye Oct. 5, 1943 2,404,772 Brodie July 30, 1946 2,420,737 De Boer May20, 1947 2,429,988 Bryant Nov. 4, 1947 2,435,920 Burroughs Feb. 10, 19482,451,317 Blair Oct. 12, 1948 FOREIGN PATENTS Number Country Date599,633 Germany Dec. 4, 1934

